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Biomedical subjects

E Richelson

Publications and source records attributed to E Richelson.

At least 163 records · Page 9Linked to original sources
PubMed1984

Antagonism by antidepressants of neurotransmitter receptors of normal human brain in vitro.

Using radioligand binding techniques, we determined the equilibrium dissociation constants (KDS) for a series of antidepressants at the histamine H1, muscarinic acetylcholine, alpha-1 and alpha-2 adrenergic and dopamine (D-2) receptors of normal human brain tissue obtained at autopsy. Twenty-five different antidepressants were studied at all but the D-2 receptor at which the number was 13 (including a metabolite of an antidepressant). Of all the receptor interactions studied, that at the histamine H1 receptor was in general the most potent interaction of this class of compounds, corresponding to results from studies using animal tissue as the source of receptors. At the human brain histamine H1 receptor, antidepressants remained among the most potent histamine H1 antagonists known, although their affinities for human receptors were lower than those for animal receptors. The most potent and the least potent compounds at the receptors were doxepin (KD = 0.24 nM) and fluvoxamine (KD = 109 microM) at the histamine H1 receptor, amitriptyline (KD = 18 nM) and trazodone (KD = 324 microM) at the muscarinic receptor, doxepin (KD = 24 nM) and viloxazine (KD = 14 microM) at the alpha-1 receptor, mianserin (KD = 73 nM) and bupropion (KD = 81 microM) at the alpha-2 receptor and amoxapine (KD = 160 nM) and trazodone (KD = 3800 nM) at the D-2 receptor, respectively. In general, compared to older drugs, the newer compounds tended to have lower affinities for these receptors.

Antidepressive Agents↗
PubMed1984

Neuroleptic affinities for human brain receptors and their use in predicting adverse effects.

Affinities of some antipsychotic drugs for 5 human brain receptors (dopamine D-2, muscarinic acetylcholine, histamine H1, alpha 1-adrenergic, and alpha 2-adrenergic receptors) were obtained using radioligand binding techniques. Seventeen drugs were studied at the D-2 receptor; 15 at the remaining receptors. These drugs showed marked differences in affinities at most receptors, and these differences may help explain variations in their propensities to cause certain adverse effects in patients. The clinical efficacy of all neuroleptics appears to be equal. Thus, these differences allow the clinician to choose drugs with low affinity for certain receptors and, thereby, minimize some of the adverse effects of these drugs in patients.

Antipsychotic Agents↗
PubMed1984

Muscarinic responses and binding in a murine neuroblastoma clone (N1E-115). Selective loss with subculturing of the low-affinity agonist site mediating cyclic GMP formation.

Cells of the murine neuroblastoma clone N1E-115 possess muscarinic receptors that influence the intracellular level of cyclic nucleotides. The stimulation of [3H]cyclic GMP levels occurs only with intact cells and has an EC50 near the "low-affinity" agonist equilibrium dissociation constant (KL) determined by radioligand binding assays. The inhibition of prostaglandin E1-stimulated [3H]cyclic AMP formation has an EC50 close to the value for the "high-affinity" agonist equilibrium dissociation constant (KH). During sequential subculturing in medium supplemented with newborn bovine serum, the inhibition of [3H]cyclic AMP was maintained, but the [3H]cyclic GMP response declined dramatically, and after 7 subculturings it was essentially absent. The time course for [3H]cyclic GMP formation in a late subculture with an 88% loss of the response was identical with the time course in early subcultures. A normal [3H]cyclic GMP response to bradykinin and histamine was demonstrated to be present in cells that had lost the [3H]cyclic GMP response to carbachol. The EC50 and KD values for the two muscarinic responses and binding sites increased 3- to 4-fold after several subculturings. A 90% loss of low-affinity binding sites was closely correlated with a similar loss of the [3H]cyclic GMP response. High-affinity binding sites did not decline significantly in concentration until the 11th subculture, where the total number of muscarinic sites was only 6% of the earliest subculture. In all subcultures, however, the ability of the muscarinic receptor to decrease [3H]cyclic AMP levels was maintained. These data, which show that the subculturing of N1E-115 cells in medium supplemented with newborn calf serum results in a selective loss of one muscarinic function, strongly support the hypothesis that these cells contain two separate muscarinic receptor-effector systems. One receptor subtype or conformation has a low affinity for the agonist and mediates cyclic GMP formation. The other receptor subtype or conformation has a higher affinity for the agonist and mediates an inhibition of prostaglandin E1-stimulated cyclic AMP formation.

Animals↗
PubMed1984

Alcohol and the elderly. Psychotropics and the elderly: interactions to watch for.

Alcohol can increase blood levels of diazepam, and probably of other benzodiazepines. Alcohol also potentiates the CNS-depressant effects of these drugs. Before adding a psychotropic drug in older patients, discontinue as many drugs as possible. Prescribe smaller doses and follow cardiovascular status. Determine serum levels when in doubt, especially with tricyclic antidepressants.

Adult↗
PubMed1983

Antidepressants are weak competitive antagonists of histamine H2 receptors in dissociated brain tissue.

Guinea pig hippocampus dissociated by mechanical means into uniform clumps of cells (approximately 100 micron in diameter) contains histamine receptors (H1 and H2) which mediate the formation of cyclic AMP. In this preparation, antidepressants are very potent antagonists of histamine H1 receptors but are weak antagonists of histamine H2 receptors. The latter result is contrary to data derived by others using homogenates of the guinea pig hippocampus and seems to dispel the idea that antidepressants derive their efficacy by blocking histamine H2 receptors in brain.

Animals↗
PubMed1983

Thrombin stimulation of guanosine 3',5'-monophosphate formation in murine neuroblastoma cells (clone N1E-115).

Thrombin, the central regulatory enzyme in coagulation, when incubated in nanomolar concentrations with murine neuroblastoma cells produced a rapid and marked increase in tritiated guanosine 3',5'-monophosphate (cyclic GMP) formation that was blocked by hirudin and competitively antagonized by dansylarginine N-(3-ethyl-1,5-pentanediyl)amide. Diisopropylphosphofluoridate-inactivated thrombin as well as the serine protease trypsin were markedly less potent and less effective than alpha-thrombin in producing this effect. Thrombin-stimulated cyclic GMP formation was inhibited by mepacrine and nordihydroguaiaretic acid but unaffected by indomethacin, suggesting that lipoxygenase metabolites of arachidonic acid are involved in the response. These results suggest that a thrombin-like protease in the brain may be involved with the function of neurons or that thrombin interactions with nerve cells, such as those following cerebral hemorrhage or other trauma of the central nervous system, may be important in the subsequent neuropathology.

Animals↗
PubMed1983

Effect of some calcium antagonists on muscarinic receptor-mediated cyclic GMP formation.

Several calcium antagonists were screened for their effect on muscarinic acetylcholine receptor-mediated cyclic GMP formation in murine neuroblastoma cells (clone N1E-115). Mn2+, Ni2+, and verapamil rapidly antagonized the response noncompetitively, with the following order of potency: verapamil greater than Mn2+ greater than Ni2+. The effects of Mn2+ and Ni2+, but not those of verapamil, were largely reversed by increasing extracellular calcium concentration. Additional effects of these agents included displacement of [3H]quinuclidinyl benzilate binding by verapamil and elevation of cyclic GMP levels by Mn2+ and Ni2+ in the absence of agonists. These results are in support of the hypothesis that receptor-mediated cyclic GMP formation by these cells is dependent upon entry of calcium into the cell and demonstrate the complexity of the effects of calcium antagonists.

Animals↗
PubMed1983

Perturbation of upper gastrointestinal function by cold stress.

To study the effects of stressful stimulus (cold pain) upon postprandial gastric, duodenal, and pancreatic function, nine healthy adult volunteers were intubated and then given two identical liquid meals, (199 cal (789 KJ) 240 ml), each being ingested during a period of irregular fasting gastroduodenal motility. Ten minutes after each meal the subjects received, in randomised order, either a test or control stimulus. The test stimulus consisted of repeated one minute immersions of a hand into ice water, with 15 seconds recovery between immersions, for a total of 20 minutes, while for the control, water at 37 degrees C was used. Serial samples of gastric and duodenal contents allowed estimation of changes in gastric emptying and acid secretion, together with pancreatic trypsin output, by a double marker perfusion technique. Measurements of blood pressure, pulse, and finger temperature acted as extra-intestinal indices of autonomic response to the stimuli. Cold pain significantly delayed gastric emptying and produced a biphasic alteration in both gastric secretion and pancreatic trypsin output, with an initial reduction during the response to the stress followed by an increase during the post-stress period. Our findings show that the normal postprandial function of the upper gut can be measurably disturbed by a stressful stimulus. The coincidence of these disturbances with other extra-intestinal autonomic changes suggests that they are a further manifestation of the somatic response to a stress.

Adult↗
PubMed1983

Antimuscarinic and other receptor-blocking properties of antidepressants.

Tricyclic antidepressants (for example, amitriptyline) and other types of antidepressants (for example, amoxapine and maprotiline) are competitive antagonists of muscarinic acetylcholine receptors, the predominant class of acetylcholine receptors in the brain. Some evidence suggests that this muscarinic receptor blockade in brain alleviates depression. However, all tricyclic antidepressants appear to be equally effective in treating depression despite having differences in their antimuscarinic potencies while having similar ranges of therapeutic blood levels. It is more likely that the antimuscarinic potency of antidepressants is related mainly to the frequency with which they cause such symptoms as blurred vision, dry mouth, and urinary retention. Information on the antimuscarinic potency and other receptor-blocking potencies of antidepressant agents can be helpful in minimizing or avoiding certain side effects when these drugs are given to patients.

Antidepressive Agents↗
PubMed1983

Antagonism by antidepressants of muscarinic acetylcholine receptors of human brain.

1 Twenty-two compounds classified as antidepressants, metabolites of antidepressants or putative antidepressants were assayed for their ability to antagonize the binding of (-)-[3H]-quinuclidinyl benzilate to muscarinic receptors in homogenates of human caudate nucleus. 2 Sixteen of these compounds were assayed for their ability to antagonize carbachol-stimulated cyclic guanosine 3',5'-monophosphate (cyclic GMP) synthesis by intact murine neuroblastoma cells (clone N1E-115). 3 Equilibrium dissociation constants (KDs) for these drugs and the muscarinic receptors of human brain spanned over 4 orders of magnitude, with the tertiary amine tricyclic antidepressant, amitriptyline (KD = 18 nM) being the most potent compound tested and trazodone (KD = 324 microM) the least potent. 4 There was a significant correlation between the data for human and murine receptors and for eight compounds (imipramine, desipramine, maprotiline, mianserin, 3-chloro-2-hydroxyimipramine, amoxapine, 2-hydroxyimipramine and iprindole). KD values measured by the two techniques were not significantly different.

Animals↗
PubMed1983

Are receptor studies useful for clinical practice?

The validity and clinical usefulness of receptor binding studies of psychotropic drugs, particularly the antidepressants, is examined. Data on the affinities of antidepressants for several different neurotransmitter receptors in human brain are presented along with other pharmacologic data on these drugs.

Animals↗
PubMed1983

Thrombin binding to human brain and spinal cord.

Thrombin, a serine protease that regulates hemostasis, has been shown to stimulate the formation of cGMP in murine neuroblastoma cells. The nervous system in vivo thus may be postulated to respond to this blood-borne factor after it breaches the blood-brain barrier, as in trauma. Human alpha-thrombin was radiolabeled with 125I and shown to bind rapidly, reversibly, and with high affinity to human brain and spinal cord. These findings indicate the presence of specific thrombin-binding sites in nervous tissue and may have important clinical implications.

Animals↗