Biomedical subjects

M A Palmatier

Publications and source records attributed to M A Palmatier.

10 recordsLinked to original sources

PubMed2004

COMT haplotypes suggest P2 promoter region relevance for schizophrenia.

A recent study found, in a large sample of Ashkenazi Jews, a highly significant association between schizophrenia and a particular haplotype of three polymorphic sites in the catechol-O-methyl transferase, COMT, gene: an IVS 1 SNP (dbSNP rs737865), the exon 4 functional SNP (Val158Met, dbSNP rs165688), and a downstream SNP (dbSNP rs165599). Subsequently, this haplotype was shown to be associated with lower levels of COMT cDNA derived from normal cortical brain tissue, most likely due to cis-acting element(s). As a first step toward evaluating whether this haplotype may be relevant to schizophrenia in populations other than Ashkenazi Jews, we have studied this haplotype in 38 populations representing all major regions of the world. Adding to our previous data on four polymorphic sites in the COMT gene, including the Val158Met polymorphism, we have typed the IVS 1 rs737865 and 3' rs615599 sites and also included a novel IVS 1 indel polymorphism, yielding seven-site haplotype frequencies for normal individuals in the 38 globally distributed populations, including a sample of Ashkenazi Jews. We report that the schizophrenia-associated haplotype is significantly heterogeneous in populations worldwide. The three-site, schizophrenia-associated haplotype frequencies range from 0% in South America to 37.1% in Southwest Asia, despite the fact that schizophrenia occurs at roughly equal frequency around the world. Assuming that the published associations found between the exon 4 Val158Met SNP and schizophrenia are due to linkage disequilibrium, these new haplotype data support the hypothesis of a relevant cis variant linked to the rs737865 site, possibly just upstream in the P2 promoter driving transcription of the predominant form of COMT in the brain. The previously described HindIII restriction site polymorphism, located within the P2 promoter, varies within all populations and may provide essential information in future studies of schizophrenia.

Catechol O-Methyltransferase↗

PubMed1999

Global variation in the frequencies of functionally different catechol-O-methyltransferase alleles.

BACKGROUND: Catechol-O-methyltransferase (COMT) has been investigated as a candidate gene in many neurologic disorders involving catecholaminergic systems. The NlaIII restriction site polymorphism (RSP) at COMT is a G<-->A (site absent<-->site present) single nucleotide polymorphism (SNP) at nucleotide 322/472 (in the short or long mRNA) that results in a Val<-->Met polymorphism at amino acid 108/158 (in soluble or membrane-bound) COMT protein and different enzyme activity levels, high for Val, low for Met. COMT enzyme activity is known to vary among ethnic groups, presumably as a result of different population frequencies of these COMT alleles. We have undertaken a direct survey of allele frequencies of this polymorphism in a global sample of populations. METHODS: We typed 1314 individuals from 30 different populations using PCR of the relevant region followed by digestion with NlaIII and electrophoresis. RESULTS: The frequencies of the low activity allele (COMT*L, NlaIII site-present) vary significantly from 0.01 to 0.62. Europeans have nearly equal frequencies of the two alleles while the COMT*H allele is much more common in populations in all other parts of the world. Sequencing in nonhuman primates indicates that COMT*H is the ancestral allele in humans. CONCLUSIONS: This is the first global survey of the COMT*L and COMT*H allele frequencies, confirming and extending earlier studies to show significant world-wide variation. This is also the first study establishing the COMT*L allele as the derived allele unique to humans. Henceforth, in any population-based association studies of this polymorphism, the control allele frequencies should be in agreement with these published values for corresponding ethnic groups.

Alleles↗

PubMed1999

Global variation of a 40-bp VNTR in the 3'-untranslated region of the dopamine transporter gene (SLC6A3).

BACKGROUND: The dopamine transporter (DAT) is the primary mechanism for dopamine clearance from the synapse in midbrain dopaminergic neurons, and the target of psychostimulant and neurotoxic drugs such as cocaine, amphetamine, and MPTP. Consequently, the gene for DAT (SLC6A3) has been the focus of many population-based case-control association studies using a 40-bp VNTR in the 3'-untranslated region. Results have differed depending on the population studied, suggesting allele frequency effects are involved. For this reason, a global survey of allele frequencies for this VNTR polymorphism was performed. METHODS: Individuals (n = 1528) from 30 populations around the world were typed for this VNTR using PCR and agarose gel electrophoresis. RESULTS: As with previous studies, the ten-repeat allele is most common, except for a Middle Eastern population in which the nine-repeat allele is most frequent. Frequencies of the nine- and ten-repeat alleles vary widely even among European populations. CONCLUSIONS: Many previous association studies have used "white" or "black" U.S. populations. However, many different ethnic groups have contributed to these populations. The large variation in allele frequencies observed in this study emphasizes the inadequacy of most past studies using the case-control design and the importance of matching patient and control populations in future association studies.

Alleles↗

PubMed1997

A latent process regression model for spatially correlated count data.

This paper proposes a regression model for spatially correlated count data that generalizes the work of Zeger (1988, Biometrika 75, 621-629) developed in a time-series setting. In this approach, spatial correlation is introduced through a latent process, and the marginal mean function may contain spatial trends and covariates. Generalized estimating equations are used to estimate and perform marginal inference on the spatial trend and covariate effects. The feasibility of this approach is demonstrated using an example of the distribution of neuronal cell counts in a laboratory culture dish.

Animals↗

PubMed1993

Dopaminergic neuronal sprouting and behavioral recovery in hemi-parkinsonian rats after implantation of amnion cells.

Cells obtained from human, monkey, or rat term amnion membrane produce an activity which, in vitro, increases process outgrowth from rat sympathetic neurons and from dopaminergic neurons of the rat ventral mesencephalon. To determine if these cells could induce sprouting of dopaminergic nerve fibers in vivo, the substantia nigra of rats was lesioned unilaterally with 6-hydroxydopamine and live-rat-term amnion cells, or killed-rat-term amnion cells were implanted into the denervated striata. A control group of rats received saline injections into the denervated striata. Rats implanted with live amnion cells had a significant decrease in turning in response to amphetamine. The lesioned and implanted striata of live-amnion-cell-implanted rats contained significantly greater areas of tyrosine hydroxylase-immunoreactive fibers than the lesioned and implanted striatum of rats in the killed-amnion-cell or saline groups. Differences in the area of tyrosine hydroxylase-immunoreactive fibers in the implanted striata or in amphetamine-induced rotation between killed amnion cell-implanted and saline-injected rats did not reach significance. Implants of live amnion cells into the striatum of a parkinsonian animal model can evoke the de novo appearance of dopaminergic fibers in the denervated striatum and behavioral recovery, most likely through a trophic mechanism.

Amnion↗

PubMed1992

A novel approach to neural transplantation in Parkinson's disease: use of polymer-encapsulated cell therapy.

Transplantation of dopaminergic neurons derived from fetal or adrenal tissue into the striatum is a potentially useful treatment for Parkinson's disease (PD). Although initially promising, recent clinical studies using adrenal autografts have demonstrated limited efficacy. The use of human fetal cells, despite promising preliminary results, is complicated by tissue availability and ethical concerns. An attractive alternative is based on encapsulating dopamine-producing cells into polymer capsules prior to transplantation. Polymer capsules can be fabricated to surround the cells with a semi-permeable and immunoprotective barrier. The semi-permeable membrane allows nutrients to enter the capsule, so the encapsulated cells will survive and function, and dopamine and other low molecular weight constituents to diffuse out into the host tissue. Thus, the technique allows use of unmatched human tissue (allografts), or even animal tissue (xenografts) without immunosuppression of the recipient. Cell-loaded polymer capsules can also be retrieved if necessary or desired. The demonstration that striatal implants of encapsulated dopamine-producing cells promote behavioral recovery in rodent and primate models of PD further suggests that cellular encapsulation may be a useful strategy for ameliorating the behavioral consequences of PD.

Adrenal Medulla↗

PubMed1987

Sympathetic neuronal destruction in macaque monkeys by guanethidine and guanacline.

To determine whether the peripheral sympathetic neurons of subhuman primates are destroyed by guanacline treatment, we treated Macaca fasicularis with 2 or 20 mg/kg of guanethidine, guanacline, or the saturated analog of guanacline (SAG) 5 times per week for 4 or 12 weeks. All monkeys given 20 mg/kg of guanethidine, guanacline, or SAG showed a marked loss of neurons in the ganglia of the peripheral sympathetic nervous system. Treatment of macaques with 2 mg/kg of the guanidinium compounds resulted in patches of small-cell infiltrate, slight neuronal loss, and degenerative alterations in the sympathetic ganglia. Neuronal alterations in sympathetic ganglia of all treated monkeys were accompanied by a prominent heterogeneous infiltrate of mononuclear cells arranged primarily in a perivascular distribution and extending into the ganglionic neuropil. Peripheral sensory ganglia were unaffected. These histological findings are similar to those described in the guanethidine-induced immune-mediated sympathectomy, which has been extensively studied in the rat.

Animals↗

PubMed1987

MHC-specific cytotoxic T lymphocyte killing of dissociated sympathetic neuronal cultures.

Experiments were conducted to determine whether neurons in culture can serve as targets for immunologic attack mediated by major histocompatibility complex (MHC)-specific cytotoxic T lymphocytes (CTLs) which recognize Class I antigens. Allogeneic C3H/He primary neuronal cultures were quickly destroyed after CTL addition, while syngeneic C57BL/6J neurons were not lysed. Alterations in the distribution of chromatin were the first ultrastructural changes that occurred, followed by loss of nuclear morphology, cytosolic changes, and eventually fragmentation of both the nucleus and cytosol. With Campenot chambers, it was possible to separate the membrane and nuclear lesions. CTLs exposed to neurites, but separated from the cell body by the chamber barrier, caused degeneration of neurites but did not cause lysis and cell death. Neuronal lysis mediated by antibody and complement appeared to be distinct from CTL-mediated lysis. These experiments demonstrate that neurons in culture are targets for MHC-specific CTLs, and therefore probably express functional levels of Class I antigens. The signal for killing by CTLs is not retrogradely transported from the neurite to the cell body, and morphologic events following CTL-neuron interaction resemble those that occur in dividing tumor target cell populations.

Animals↗

PubMed1986

Species and structural specificity of the lipopigment accumulation and neuronal destruction induced by N-(2-guanidinoethyl)-4-methyl-1,2,5,6-tetrahydropyridine (guanacline).

Guanacline, a guanidinium adrenergic neuron blocking agent similar to guanethidine, was studied clinically and experimentally during the late 1960s. Like guanethidine, it has been reported to produce sympathetic neuronal destruction in rats. Unlike guanethidine, it has been reported to produce irreversible sympathetic deficits in man and to produce fluorescent lipopigment in rat sympathetic neurons. Guanacline and its derivative in which the double bond of the tetrahydropyridine ring is reduced (saturated analog of guanacline, SAG) were prepared. Several species were treated chronically with varying doses of guanethidine, guanacline or SAG; the superior cervical ganglia were examined light microscopically for neuronal destruction and for osmiophilic fluorescent lipopigment accumulation. All 3 drugs produced rapid neuronal destruction in rats accompanied by massive small-cell infiltration. In striking contrast, treatment for many weeks with doses up to 100 mg/kg/day produced no small-cell infiltration or apparent neuronal destruction in mice or guinea pigs. The neuronal destruction produced by guanacline and SAG in the rat, like that caused by guanethidine, was prevented by immunosuppression or gamma-irradiation, indicating that all 3 agents produce neuronal destruction in rats by an immune-mediated mechanism. Thus, the ability of the drug to produce sympathectomy is species specific but not drug specific. The opposite was found with respect to fluorescent lipopigment accumulation. Guanacline, but not guanethidine or SAG, produced fluorescent lipopigment in all species examined. Therefore, the double bond of the tetrahydropyridine ring plays a critical role in the production of the fluorescent lipopigment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Demonstration of retrogradely transported endogenous nerve growth factor in axons of sympathetic neurons.

The presence of retrogradely transported endogenous nerve growth factor (NGF) in sympathetic nerves of the guinea pig was demonstrated directly by fluorescent and peroxidase immunohistochemistry in the ligated superior postganglionic nerve of the superior cervical ganglion. Fixed, frozen sections of previously ligated nerve were incubated with either rabbit antiserum against guinea pig NGF (gpNGF), rabbit antibodies against gpNGF purified on a mouse NGF (mNGF) affinity column, the portion of rabbit antiserum against gpNGF that did not bind to the mNGF affinity column, or nonimmune rabbit serum. Positive staining on the peripheral side of the ligation was obtained only with unfractionated antiserum against gpNGF and with purified antibodies against gpNGF. The staining properties of the various antiserum preparations correlated with their ability to block gpNGF- and mNGF-induced neurite outgrowth in the embryonic chick dorsal root ganglion bioassay and in the PC12 bioassay. Homogenates of superior postganglionic nerve supported growth of embryonic chick dorsal root ganglia and differentiation of PC12 cells. This support was blocked by the specific antisera against NGF used in the immunohistochemistry experiments. These experiments demonstrate that endogenous NGF, presumably released by peripheral target tissues, is retrogradely transported in vivo.

Animals↗