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G S Roth

Publications and source records attributed to G S Roth.

At least 127 records · Page 7Linked to original sources
PubMed1992

Selective susceptibility of cultured striatal neurons to kainic acid.

Previous work has shown a selective sensitivity of striatal D2-receptor-containing neurons (D2 cells) to kainic acid (KA). In order to see whether this phenomenon exists in cultured cells, which could provide a very accessible model for subsequent mechanistic studies, we examined striatal cultures grown for up to 30 days and labeled with either [3H]spiperone, for D2 receptors, or with [3H]-SCH23390, for D1 receptors. Analysis of the cells was performed with a digital imaging system (RAS). The cultured cells were examined for ligand binding to receptors, cell size, and susceptibility to KA. The D2 cells showed an increased mortality over D1-receptor-containing neurons (D1 cells) in the presence of KA, of a magnitude similar to in vivo loss, with larger D2 cells showing the greatest vulnerability.

Aging↗
PubMed1992

Age-related changes in the mechanisms of LHRH-stimulated LH release from pituitary cells in vitro.

In vitro release of LH in response to LHRH, phorbol myristate acetate (PMA), the ionophore A23187, and nifedipine was evaluated in primary cultures of anterior pituitary cells from intact mature (6 to 7 month) and old (23 to 24 month) male Wistar rats. LH release from pituitary cells is reduced approximately 30% and 60% after 4 and 48 h of 10(-7) M LHRH stimulation in cells of old rats, respectively. This impairment may be secondary to a loss of LHRH receptors. LHRH-stimulated LH release from cells of mature rats was inhibited 70% by the voltage-gated calcium channel blocker, nifedipine (10(-6) M), whereas LHRH-stimulated LH release from cells of old rats was too low to detect the effects of this drug. Age changes can be partially reversed by A23187 and PMA during 4 h, but not 48 hrs of stimulation. It therefore appears that short- and long-term (4 h and 48 h, respectively) stimulation of LH release may proceed through separate mechanisms that are differentially affected by aging.

Aging↗
PubMed1992

Plasma concentrations of glucose, insulin, and percent glycosylated hemoglobin are unaltered by food restriction in rhesus and squirrel monkeys.

Plasma concentrations of glucose and percentage of glycosylated hemoglobin have been reported to be reduced in food-restricted rats when compared with ad libitum-fed controls (Masoro et al., 1989). A similar experiment in primates, in which we also measured plasma insulin, is reported in this article. Rhesus and squirrel monkeys were fed either ad libitum or 30% less than weight-matched controls for up to 36 months. No significant age or diet effects on plasma concentration of glucose, insulin, or percentage glycosylated hemoglobin were observed, except that glucose concentration decreased with age in ad libitum-fed rhesus monkeys. Moreover, no correlations between glucose levels and the percentage of glycosylated hemoglobin could be established within any group of animals. These results suggest possible differences in glucose-related metabolism in ad libitum and food-restricted primates as compared to observations made in rats.

Aging↗
PubMed1992

Altered coupling of alpha 1-adrenergic receptor-G protein in rat parotid during aging.

A possible role for altered signal transduction mechanisms in impaired alpha 1-adrenergic-stimulated secretory function during aging was investigated in parotid cells prepared from adult (6 mo) and old (24 mo) rats. Compared with adults, epinephrine-stimulated 45Ca2+ efflux and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production were reduced 31 and 36% in cells of old rats, respectively. There was a highly significant correlation between 45Ca2+ efflux and Ins(1,4,5)P3 production. In saponin-permeabilized cells, no significant differences in Ins(1,4,5)P3-stimulated 45Ca2+ efflux in adult and old preparations were observed. When G proteins were stimulated by guanosine 5'-O-(3-thiotriphosphate) or NaF, no age differences in Ins(1,4,5)P3 production were detected. Stimulation of phosphoinositide-specific phospholipase C (PLC) by CaCl2 in adult and old cells was also comparable. Moreover, no differences in immunolabeled common alpha (GTP binding site), Gi alpha, PLC-gamma, or PLC-delta could be detected in either cytosol or membranes of adult and old preparations. In the absence of 5'-guanylylimidodiphosphate [Gpp(NH)p], no age-related changes in epinephrine competition for [3H]prazosin binding sites were observed. Approximately 30% of the agonist binding sites existed in a high-affinity form at both ages. Gpp(NH)p caused large rightward shifts of epinephrine displacement curves in adult membranes (converting all binding sites to the low-affinity form), but not old. Moreover, epinephrine was much more effective in stimulating G protein low-Km GTPase in parotid membranes from adult than old rats. These data suggest that age-related impairments in alpha 1-adrenergic responsiveness are mediated, at least in part, by the functional alterations in the coupling of G proteins with alpha 1-adrenergic receptors.

Aging↗
PubMed1991

Alpha 1-adrenergic and muscarinic-cholinergic stimulated inositol trisphosphate production may proceed through different post-receptor signal transduction pathways in parotid acini.

Maximal stimulation of inositol 1,4,5 trisphosphate (IP3) production by epinephrine and carbachol in rat parotid cell aggregates is additive when the two agents are employed simultaneously. The additive response proceeds through both the alpha 1-adrenergic and muscarinic-cholinergic signal transduction pathways. It is critical that IP3 be measured by a radioreceptor assay, since when cells are labeled with 3H-inositol and IP3 determined by ion exchange chromatography, additivity is not detectable. Reasons for the discrepancy between methods are discussed. These results, coupled with the differential sensitivity of the alpha 1-adrenergic and muscarinic cholinergic pathways to neomycin and aging, suggest that they may be dissociated at the post-receptor level.

Animals↗
PubMed1991

Loss of D2 receptors during aging is partially due to decreased levels of mRNA.

Corpora striata of old rats (24-25 months) contain only about half as much mRNA for D2 dopamine receptors as those of young (6 months) counterparts. This reduction can be observed by in situ hybridization of brain slices as well as with Northern and dot blot analyses of striatal extracts. Decreased levels of D2 receptor mRNA as described in this study are consistent with reductions in receptor containing neurons (20%) and receptor biosynthesis (40%), as previously observed in this and other laboratories. Thus, age related changes in D2 receptor gene expression appear to be partially responsible for loss of these receptors.

Aging↗
PubMed1991

The deleterious effects of aging and kainic acid may be selective for similar striatal neuronal populations.

The present experiments were performed to determine whether the age-related loss of striatal D2 receptors could be localized to a kainic acid-sensitive neuronal population. This neurotoxin selectively destroys intrinsic neurons. Thus, if kainic acid reduced striatal D2 receptor concentrations such that age differences in this parameter were no longer observed, it would be a good indication that the D2 receptors lost through aging are also sensitive to kainic acid. Mature (6 months) and senescent (24 months) rats were stereotaxically, unilaterally injected with 3 micrograms/0.5 microliter kainic acid into the right striatum. Seven days later striatal D2 receptors were assessed with [3H]-spiperone in one group of mature and senescent rats. A second group of mature and senescent unilaterally lesioned rats was anesthetized and perfused. Brains were dissected and processed for striatal cell counts using cresyl violet staining, tyrosine hydroxylase and met-enkephalin using immunocytochemistry, and acetylcholinesterase using histochemistry. Age-related differences in D2-receptor concentrations were observed in intact, but not lesioned, striata. Kainic acid was less effective in reducing D2-receptor concentrations in senescent animals, suggesting that some proportion of the receptors was already lost prior to lesioning. Kainic acid also reduced total neuronal numbers, as well as Met-Enk and AChE positive staining, to approximately the same extent in mature and senescent rats. No age differences were seen in any of the other parameters following kainic acid administration.

Acetylcholinesterase↗
PubMed1990

Selective cross-activation/inhibition of second messenger systems and the reduction of age-related deficits in the muscarinic control of dopamine release from perifused rat striata.

Possible alterations in muscarinic cholinergic (mACh) signal transduction in senescence were studied in rat neostriata. Acetylcholine (ACh) activation of striatal muscarinic heteroreceptors by carbachol or oxotremorine enhances K(+)-evoked release of dopamine from perifused striata of 6- but not 24-month-old rats. Present experiments determined the effects of simultaneous activation or activation/inhibition of more than one second messenger on K(+)-evoked release of DA from perifused striatal slices from these age groups. Combinations of carbachol (500 microns), which stimulates inositol-1,4,5-bisphosphate (IP3) production and inhibits cyclic AMP production, with oxotremorine (500 microns), which inhibits cyclic AMP production, in the presence of 30 mM KCl (in a modified Krebs-Ringer medium) reduced the age-related reduction in mAChR enhancement of DA release (analyzed by HPLC coupled to electrochemical detection; 5 min fractions were collected on ice in perchloric acid; flow rate 120 microliters/min). Combinations of these agonists with the putative second messenger arachidonic acid (10 microM), also enhanced K(+)-evoked release of DA in the striatal tissue from the 24-month group. IP3 activation was lower in the striatal tissue from old animals than those from young under all conditions, but cross-activation/inhibition actually may have lowered the IP3 threshold necessary for enhanced DA release to occur. In a subsequent experiment, pre-loading striatal tissue from young animals with either carbachol or oxotremorine under basal release conditions reduced the responding when the basal release medium was switched to one containing 30 mM KCl and combinations of the agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

Discordant effects of aging on prolactin and luteinizing hormone-beta messenger ribonucleic acid levels in the female rat.

To examine the molecular genetic basis for the age-related increase in PRL secretion and decrease in LH production in the rat, we measured steady state levels of PRL and LH beta mRNA in pituitary homogenates and cell lysates from monolayer adenohypophyseal cultures. These mRNA levels were compared with the corresponding levels of immunoreactive PRL and LH in sera and culture media. Paired groups (n = 4-10/group) of intact and 4-week ovariectomized mature (6-7 months old) and old (23-25 months old) female Wistar rats were studied. Serum PRL levels were 550% higher in intact old vs. mature rats (P less than 0.001), whereas the corresponding pituitary homogenate levels of PRL mRNA were similar (P greater than 0.4). Medium PRL concentrations were 230% greater (P less than 0.006) whereas cell lysate concentrations of PRL mRNA were unaltered (P greater than 0.2) in monolayer cultures from intact old vs. mature rats. Serum PRL levels were 650% higher (P less than 0.003) and pituitary homogenate PRL mRNA levels were slightly increased (P less than 0.04) in ovariectomized old vs. mature rats. Neither serum LH values (P greater than 0.07) nor pituitary homogenate LH beta mRNA levels (P greater than 0.1) differed in intact old and mature rats, whereas the corresponding medium concentrations of LH were reduced (P less than 0.001). Ovariectomized old vs. mature rats exhibited reductions in serum (P less than 0.02) and medium (P less than 0.001) LH concentrations, as well as in pituitary homogenate (P less than 0.002) and cell lysate (P less than 0.006) LH beta mRNA levels. Thus, these data revealed coordinate decreases with age in LH beta mRNA and LH secretion, particularly in ovariectomized rats, suggesting an age-related alteration at or before LH beta gene transcription. These findings parallel observations on other genes whose products change with age. In contrast, the observation that the increased secretion of PRL in old rats is accompanied by little or no increase in PRL mRNA is novel and suggests that age-related alterations in PRL gene expression proceed through a posttranscriptional mechanism.

Aging↗
PubMed1989

Reduction of motor behavioural deficits in senescence via chronic prolactin or estrogen administration: time course and putative mechanisms of action.

The effects of chronic estrogen (E2), rat prolactin (rPRL), modified ovine prolactin (mPRL) administration on motor behavior (inclined screen performance) and striatal dopamine (DA) (D2subtype) receptor concentrations were examined in senescent (greater than 24 months of age) female rats, mPRL possesses no lactotrophic activity. Administration of either E2 or rPRL was effective in improving both inclined screen performance (increased time that the animal could remain on the screen by 95 and 413 s, respectively, compared to highest pre-injection performance) and striatal D2 receptor concentrations (14 and 20% respectively). These were indications, however, from separate analyses that improvements in inclined screen performance were seen prior to any increases in striatal D2 receptor concentrations. These early performance increases seemed instead to be the result of improved muscarinic receptor control over striatal DA autoreceptor function. Later improvements in inclined screen performance (at 6-7 days after the E2 injections were begun) were more dependent on increased striatal DA receptor concentrations. A second set of experiments which involved the injection of E2 into senescent male as well as female rats indicated that there were no sex differences in improvements in inclined screen performance, and that once the E2 injections were discontinued, performance returned to preadministration levels. The results are discussed in terms of two important processes that may be involved in mediating enhanced inclined screen performance following E2 administration: (1) enhancement of muscarinic receptor regulation of DA autoreceptor function; and (2) increases in striatal DA receptor density.

Aging↗
PubMed1989

Evidence for an alteration in the microsomal Ca2+ release mechanism in senescent rat parotid acinar cells.

Previously, we have shown that Ca2+ mobilization following an alpha 1-adrenergic receptor stimulus is reduced in parotid acinar cells from senescent rats as a result of an altered ability of inositol 1,4,5-trisphosphate (IP3) to induce Ca2+ release from a non-mitochondrial, intracellular Ca2+ store (Ishikawa, Y., et al. Biochim. Biophys. Acta 968, 203-210). We have used this model to examine the IP3-induced Ca2+ release mechanism in these cells. 45Ca2+ efflux, after exposure to (-) epinephrine, from cells of young adult (3-6 months) rats was approx. 2-fold that observed from cells from older animals (approx. 24 months) either in the presence or absence of extracellular Ca2+. Similarly, cytosolic Ca2+ levels were greater in cells of young adult rats under these same incubation conditions. However, microsomal membrane preparations, from both age groups displayed similar IP3 binding sites (Kd approximately 90 nM, Bmax approximately 850 fmol/mg protein) and ATP-dependent Ca2+ transport ability (approx. 8 nmol/mg protein.min -1). These data suggest that there is an alteration in the IP3-induced Ca2+ release mechanism in microsomal membranes of parotid glands from senescent rats which may account for the decreased Ca2+ release seen after agonist stimulation of this tissue.

Animals↗
PubMed1989

Effect of aging on concentrations of D2-receptor-containing neurons in the rat striatum.

Striatal D2 dopamine receptor concentrations were shown to decrease 30-35% during the lifespan of Wistar rats as assessed both radiochemically and autoradiographically. Binding densities and degree of age-change varied within the striatum; the latter ranging from 17 to 44% in 4 different regions. Overall neuronal loss during aging was 19%, and also varied considerably within the different striatal regions. Thus, it appears that neuronal loss may account for up to roughly half of the striatal D2 receptor loss during aging.

Aging↗
PubMed1989

Dissociation of alpha-adrenergic and cholinergic stimulated inositol trisphosphate-dependent calcium mobilization at the "post-receptor" level.

Carbachol stimulated inositol trisphosphate (IP3) production and subsequent calcium mobilization in parotid cells are almost completely inhibited by neomycin. In contrast epinephrine stimulated IP3 production and calcium mobilization are much less sensitive to such inhibition. Since neomycin exerts its effects primarily at the level of inositol phosphate production and action, cholinergic and alpha adrenergic stimulation of IP3 dependent calcium mobilization may proceed through different "post-receptor" signal transduction mechanisms in parotid cells.

Animals↗
PubMed1989

Effect of aging on populations of estrogen receptor-containing cells in the rat uterus.

Estrogen receptor-containing cells were identified in uteri of mature and senescent rats by means of quantitative autoradiography. Cell numbers and density were assessed in the various uterine layers. It was determined that despite decreases in receptor concentrations in endometrium, endometrial stroma, myometrium, and epithelium, no significant cell loss occurred in any region. Receptor content per cell clearly decreased with age in the endometrial stroma, while only in the myometrium was there any suggestion of cell loss in the absence of receptor loss from individual cells. Thus, age-related reductions in uterine estradiol receptor levels may be due to different mechanisms in different tissue regions.

Aging↗