Search PubMed⌕ Search

Biomedical subjects

E Richelson

Publications and source records attributed to E Richelson.

At least 91 records · Page 5Linked to original sources
PubMed1992

The rat neurotensin receptor expressed in Chinese hamster ovary cells mediates the release of inositol phosphates.

To study second messenger synthesis mediated by the cloned rat neurotensin receptor, we derived a cell line stably expressing this receptor. The cDNA clone of this receptor was subcloned into the pcDNA1neo expression vector. This construct was then used to transfect Chinese hamster ovary (CHO)-K1 cells. Colony clones, selected for resistance to antibiotic G-418 sulfate, were isolated and grown separately. Nineteen individual clones were screened for total [3H]neurotensin binding as an indication of neurotensin receptor expression. The clone (CHO-rNTR-10) showing the highest level of specific [3H]neurotensin binding was characterized further. With intact cells, the equilibrium dissociation constant (KD) for specific [3H]neurotensin binding was 18 nM, and the maximal number of binding sites (Bmax) was 900 fmol/mg of protein or 740 fmol/10(6) cells (approximately 4.4 x 10(5) sites on the cellular surface). Whereas the KD was similar to that found in other cellular systems, for example, the murine neuroblastoma clone N1E-115, the Bmax exceeded previously reported values. Incubation of intact CHO-rNTR-10 cells with neurotensin caused the release of inositol phosphates in a dose-dependent manner (EC50 = 3 nM), results indicating that the expressed transfected receptor was functional. Neurotensin did not inhibit cyclic AMP levels stimulated by forskolin. As with other systems, neurotensin (8-13) was more potent than neurotensin Neurotensin-mediated inositol phosphate release is the first report of second messenger synthesis for this receptor expressed in a transfected cell line. These results suggest that the relation between structure and function of the neurotensin receptor can be readily studied in transfected cell lines.

Animals↗
PubMed1992

Antagonism by antimuscarinic and neuroleptic compounds at the five cloned human muscarinic cholinergic receptors expressed in Chinese hamster ovary cells.

We determined the affinity and selectivity of binding for 24 compounds: nine antimuscarinics (including some antiparkinson drugs) and 15 neuroleptics (including the atypical compounds clozapine, fluperlapine, melperone, rilapine, risperidone, tenilapine, tiosperone and zotepine) at the five human muscarinic receptor subtypes expressed in Chinese hamster ovary cells. Equilibrium dissociation constants (Kd) were obtained from competitive radioligand binding studies with [3H]quinuclidinyl benzilate and membranal preparations of these cells. As expected, QNB had the highest affinity of the compounds studied at the five receptor subtypes and was not selective (Kd ranged from 0.027-0.088 nM). Benztropine had the next highest affinity of the antimuscarinic compounds and thioridazine had the highest affinity of the neuroleptics. Among the antiparkinson drugs, biperiden was the only one selective for the m1 subtype; and among the neuroleptics, the atypical drug clozapine was also selective for the m1 subtype. This selectivity may explain clozapine's unusual efficacy in refractory schizophrenic patients and its low incidence of extrapyramidal side effects. However, because most other atypical neuroleptics studied lacked high affinity and selectivity at muscarinic receptor subtypes, it is likely that other mechanisms are involved as well.

Animals↗
PubMed1991

Structure-antinociceptive activity of neurotensin and some novel analogues in the periaqueductal gray region of the brainstem.

Neurotensin, an endogenous tridecapeptide, produces a potent, naloxone-insensitive antinociceptive response when it is microinjected into the periaqueductal gray region of the rat brainstem. In the present study, the ED50 for neurotensin in inducing antinociception was 1.5 nmol, two times more potent than morphine. We sought to find whether neurotensin's antinociceptive effects were mediated by the same receptor that mediates its other functions. We found that the structure-activity relationship of neurotensin-induced antinociception was different from that required for the stimulation of intracellular cyclic GMP production in neuroblastoma clone N1E-115 and the binding to N1E-115 cells, human brain tissue, or rat periaqueductal gray. These data suggest there exists a subtype of neurotensin receptors in neural tissue that mediates its antinociceptive actions.

Analgesics↗
PubMed1991

Developmental regulation of neurotensin receptor expression and function in murine neuroblastoma clone N1E-115.

Murine neuroblastoma cells (clone N1E-115) during their growth from log to late stationary phase, expressed no specific neurotensin binding sites until day 7 in culture. From day 7 to day 20, binding sites increased 6-fold in number/cell and more than 4-fold in sites/mg protein. Neurotensin-mediated cyclic [3H]GMP synthesis was not detected until day 17. For these cells these data show that neurotensin receptor binding and function are regulated with respect to growth cycle and that presence of neurotensin binding sites is not sufficient for receptor function.

Animals↗
PubMed1991

Reduced D2 dopamine and muscarinic cholinergic receptor densities in caudate specimens from fluctuating parkinsonian patients.

Binding of spiperone and 3-quinuclidinyl benzilate (QNB), both labeled with hydrogen 3 (3H), were measured in caudate tissue obtained from 8 living parkinsonian patients at the time of cerebral transplantation. This was clinically homogeneous group of patients. All remained predominantly responsive to levodopa, although with marked disability secondary to clinical fluctuations (short-duration responses) and medication-induced dyskinesias; all were receiving substantial doses of levodopa and 6 of the 8 patients were additionally receiving bromocriptine or pergolide. Binding densities of dopamine D2 receptors, as measured by [3H]spiperone binding, were reduced in this group of patients, compared to caudate specimens from autopsy control subjects. This findings may reflect medication-induced receptor downregulation. Parallel changes occurred with muscarinic cholinergic receptors; [3H]QNB binding was significantly reduced, compared to autopsy control values. This reduction of muscarinic receptors might be due to loss of nigrostriatal terminals that are known to contain muscarinic receptors. Alternatively, muscarinic receptors may have been downregulated by increased corticostriatal glutamatergic input to cholinergic cells, inferred to be present based on the prominent levodopa-induced dyskinesias. Finally, receptor deficits could have been a reflection of more widespread degenerative cerebral disease, although levodopa-refractory symptoms were generally not pronounced in these patients.

Adult↗
PubMed1991

Selectivity of antimuscarinic compounds for muscarinic receptors of human brain and heart.

Seven antimuscarinic compounds, used mostly for the treatment of extrapyramidal problems, were tested in vitro in radioligand binding assays for evidence of selectivity for two different pharmacological subtypes of the human muscarinic receptor, M1, a predominant form in brain, and M2, a predominant form in heart. Although biperiden, scopolamine, procyclidine, and benztropine showed significant selectivity in the in vitro assays, it is likely that in clinical practice biperiden would be the drug of choice to avoid any antimuscarinic effects on the heart.

Brain↗
PubMed1991

Potentiation by a sodium channel activator of effects of lithium ion on cyclic AMP, cyclic GMP and inositol phosphates.

The effects of the lithium ion (Li+) on receptor-mediated synthesis of second messengers were determined, when cellular sodium channels were quiescent or excited, using the murine neuroblastoma clone (N1E-115). In this clone, lithium inhibited the receptor-mediated synthesis of cyclic AMP and cyclic GMP and it also increased the accumulation of inositol phosphates by a receptor-mediated process. When veratridine (20 microM) excited the sodium channel, the effects of lithium were potentiated. However, tetrodotoxin, a sodium channel blocker, completely prevented this potentiation. These results suggest that when neurons are depolarizing actively and intraneuronal levels of lithium increase by entry through the sodium channel, lithium has a more potent intracellular effect. As a result, lithium would have more potent and selective effects in those pathologically-active neurons underlying manic-depressive disorder.

Animals↗
PubMed1991

Neuroleptic binding to muscarinic M2 receptors of normal human heart in vitro and comparison with binding to M1 and dopamine D2 receptors of brain.

We determined by radioligand binding the equilibrium dissociation constants (Kd's) for seventeen neuroleptics at muscarinic M2 receptors of human heart atrium and compared these data with our previous data for binding to muscarinic M1 and dopamine D2 receptors of human brain. At the M2 receptor, the most potent compound was thioridazine; the least, molindone. If selectivity is defined as Kd at one receptor less than or equal to 0.1 Kd at the other receptor, no compound was selective for the M2 subtype. Two compounds, clozapine and triflupromazine, were selective for the M1 subtype. Thus, few neuroleptics have the assumed preferred property of M1 over M2 subtype selectivity. Such a feature could reduce extrapyramidal side effects, while reducing the likelihood of certain cardiac side effects.

Antipsychotic Agents↗
PubMed1991

Two possibly distinct prostaglandin E1 receptors in N1E-115 clone: one mediating inositol trisphosphate formation, cyclic GMP formation, and intracellular calcium mobilization and the other mediating cyclic AMP formation.

Prostaglandin E1 (PGE1)-mediated transmembrane signal control systems were investigated in intact murine neuroblastoma cells (clone N1E-115). PGE1 increased intracellular levels of total inositol phosphates (IP), cyclic GMP, cyclic AMP, and calcium ([Ca2+]i). PGE1 transiently increased inositol 1,4,5-trisphosphate formation, peaking at 20 s. There was more than a 10-fold difference between the ED50 for PGE1 at cyclic AMP formation (70 nM) and its ED50 values at IP accumulation (1 microM), cyclic GMP formation (2 microM), and [Ca2+]i increase (5 microM). PGE1-mediated IP accumulation, cyclic GMP formation, and [Ca2+]i increase depended on both the concentration of PGE1 and extracellular calcium ions. PGE1 had more potent intrinsic activity in cyclic AMP formation, IP accumulation, and cyclic GMP formation than did PGE2, PGF2 alpha, or PGD2. A protein kinase C activator, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, had opposite effects on PGE1-mediated IP release and cyclic GMP formation (inhibitory) and cyclic AMP formation (stimulatory). These data suggest that there may be subtypes of the PGE1 receptor in this clone: a high-affinity receptor mediating cyclic AMP formation, and a low-affinity receptor mediating IP accumulation, cyclic GMP formation, and intracellular calcium mobilization.

Animals↗
PubMed1991

Biological basis of depression and therapeutic relevance.

Before the advent of the pharmacologic treatment of depression, there were theories about the biological basis of affective disorders. However, today's theories are derived largely from known pharmacologic effects of antidepressants. These effects, derived from neurochemical studies with laboratory animals, have implicated catecholamines and serotonin in depression. Although most antidepressant drugs in use today have been available for decades, their mechanism of action in treating depression has not been established. In addition, theories about the biological causes of depression have not been proven. Nevertheless, the rich pharmacology for antidepressant drugs involving blockade of neuronal uptake systems for some biogenic amines and blockade of many receptors for neurotransmitters can explain some of their adverse effects and certain interactions with other drugs.

Antidepressive Agents↗
PubMed1991

Binding of benzodiazepines and some major metabolites at their sites in normal human frontal cortex in vitro.

Using [3H]flunitrazepam in radioligand binding assays, we determined equilibrium dissociation constants (Kd's) at 37 degrees C for 22 benzodiazepines (15 parent compounds and 7 major metabolites) at benzodiazepine binding sites in human frontal cortex. This list included several compounds never studied before at human receptors. Although dissociation was too rapid to measure reliably at this temperature, the Kd's for flunitrazepam were not significantly different when either rapid filtration or centrifugation was used to separate the bound from free radioligand. The most potent compound was triazolam (Kd = 0.54 nM); the least potent, chlordiazepoxide (Kd = 684 nM). The Kd's were significantly lower (about 3- to 7-fold) for several compounds tested at an equilibrium temperature of 0 degrees C compared to those obtained at 37 degrees C. There was a strong correlation for 15 compounds for the log Kd at rat brain receptors (data obtained from the literature) vs. the log Kd for human brain. In addition, the log Kd's of the various benzodiazepines for their receptor were significantly correlated with the log of their minimum daily dosages used to treat patients. Many of the benzodiazepines have clinically important active metabolites that have higher affinity for benzodiazepine binding sites in human brain than their parent compounds. Such data have important implications in the clinical use of these compounds.

Aged↗
PubMed1990

Desensitization of muscarinic M1 receptors of murine neuroblastoma cells (clone N1E-115) without receptor down-regulation and protein kinase C activity.

Acute desensitization of M1 muscarinic receptor-mediated responses (cyclic GMP formation and inositol phosphate release) was studied in murine neuroblastoma cells (N1E-115 clone). After a 45-min incubation at 37 degrees of N1E-115 cells either in monolayer or in suspension, with the muscarinic agonist carbachol (1 mM), the receptor-mediated cyclic GMP response to carbachol was nearly completely lost. This loss was associated with greater than 80% loss of carbachol-mediated inositol phosphate release. The protein kinase C activator phorbol 12-myristate 13-acetate (PMA) inhibited both responses with similar potencies. Carbachol or PMA reduced by 30-40% the number of muscarinic receptor sites for antagonist and agonist on intact cells (determined in binding assays using [3H]N-methylscopolamine) only for cells in monolayer and not for those in suspension. PMA but not carbachol pretreatment of cells in monolayer or in suspension caused a translocation of [3H]phorbol 12,13-dibutyrate binding and protein kinase C activity. In addition, desensitization to carbachol occurred in cells largely depleted of protein kinase C by chronic exposure to PMA. Thus, agonist-mediated down-regulation is not needed for muscarinic M1 receptor desensitization, which may be a result of the activation of a receptor-activated kinase different from protein kinase C.

Animals↗
PubMed1990

Cardiovascular effects of neurotensin and some analogues on rats.

When administered in vivo into the femoral vein of normotensive rats, neurotensin, neurotensin-(8-13), and [D-Lys8]neurotensin-(8-13) decreased diastolic blood pressure in a dose-dependent manner, without change in heart rate. All three peptides evoked tachyphylaxis and a triphasic depressor-pressor-depressor, response at higher doses. The rank order of potency was neurotensin greater than [D-Lys8]neurotensin-(8-13) greater than neurotensin-(8-13). In organ chamber experiments, both neurotensin and neurotensin-(8-13) at a range of concentrations which induced dose-dependent decreases in blood pressure, did not significantly change tension in rat aorta rings with or without endothelium. In contrast, [D-Lys8]neurotensin-(8-13) induced weak dose-dependent relaxation of both rings with or without endothelium. However, this effect was not obtained at concentrations able to decrease the blood pressure. Indomethacin did not change the vasodilator effect of [D-Lys8]neurotensin-(8-13). There was no correlation between the vasodilator effect of this peptide and its ability to decrease blood pressure. These experiments suggest that the hypotension was not due to a direct vasodilator effect on the smooth muscle. In addition, since the rank order of peptide potency was opposite of those found in previous studies of second messenger synthesis and binding to neural tissue, these data suggest that there is a second receptor for neurotensin or that neurotensin can also bind to a different unknown receptor.

Animals↗