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Biomedical subjects

A M van Delft

Publications and source records attributed to A M van Delft.

At least 19 recordsLinked to original sources
PubMed1996

Differences in modulation of noradrenergic and serotonergic transmission by the alpha-2 adrenoceptor antagonists, mirtazapine, mianserin and idazoxan.

The effects of three compounds with alpha-2 adrenoceptor antagonistic properties, mirtazapine (Org 3770; Remeron), mianserin and idazoxan, were measured on hippocampal noradrenergic and serotonergic transmission in freely moving rats by using microdialysis. Dihydroxyphenylacetic acid (DOPAC) was measured as a correlate of noradrenergic presynaptic activity. Infusing 1 microM tetrodotoxin decreased extracellular serotonin (5-HT) and DOPAC by 65 and 40%, respectively. 5-Hydroxytryptophan (25 mg/kg s.c.) increased extracellular 5-HT by 500%, whereas 8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (0.5 mg/kg s.c.) decreased 5-HT release by 60%. Prazosin decreased 5-HT release to 60% of base-line in agreement with an alpha-1-mediated control of 5-HT transmission, whereas it increased DOPAC release with 80%. Both mirtazapine (2 and 5 mg/kg s.c.) and idazoxan (1 mg/kg s.c.) caused a rapid increase in DOPAC by up to 80%. Mianserin slowly increased DOPAC, reaching a maximal increase of 30 and 60% at 2 and 5 mg/kg s.c., respectively. Only mirtazapine caused a concurrent increase in 5-HT, reaching up to 80% above base-line within 60 min, whereas mianserin and idazoxan failed to change 5-HT levels significantly. Mirtazapine (5 mg/kg s.c.) only slightly affected DOPAC and homovanillic acid levels in the striatum, hardly affected 5-HT release, but clearly increased 5-hydroxyindole acetic acid. Thus, the antidepressants mirtazapine and mianserin markedly differ in their effects on noradrenergic and serotonergic transmission in vivo as measured with microdialysis in freely moving rats. These differences are explained by their different modulatory effects on noradrenergic transmission.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1994

Genomic organisation and functional expression of the gene encoding the human serotonin 5-HT2C receptor.

The 5-HT2C receptor gene is unique among the members of the 5-HT receptor family by virtue of its genomic organisation. The human 5-HT2C receptor gene, unlike many other genes for guanine nucleotide binding (G)-proteins, contains three introns which interrupt the coding sequence into four exons. The first two introns are at equivalent positions as compared to the intervening sequences previously found in the 5-HT2(A) receptor gene, suggesting a close evolutionary relationship between both genes. Southern blot analysis shows that the 5-HT2C receptor gene is a single copy gene. Furthermore, we report the functional expression of a complementary DNA for the 5-HT2C receptor, cloned from hippocampal RNA. Membranes prepared from NIH 3T3 cells stably expressing the 5-HT2C receptor cDNA, displayed a single population of high affinity sites for the antagonist [3H]mesulergine (Kd = 2.9 +/- 0.4 nM, Bmax = 44.3 +/- 7.2 pmol/mg protein) as well as for [3H]5-HT (Kd = 9.9 +/- 0.7 nM, Bmax = 13.6 +/- 1.0 pmol/mg protein). Displacement of [3H]mesulergine and [3H]5HT binding by ligands indicated a pharmacological similarity of these binding sites with porcine and rat choroid plexus 5-HT2C receptors. Furthermore, activation of the 5-HT2C receptor with 5-HT results in an increased phospholipase C activity.

3T3 Cells↗
PubMed1994

Reversal by NGF of cytostatic drug-induced reduction of neurite outgrowth in rat dorsal root ganglia in vitro.

Cytostatic drugs, like cisplatin, vincristine and taxol, when given to cancer patients may cause peripheral neuropathies. We were interested in the potential neuroprotective effects of neurotrophic factors against such neuropathies. To this aim we studied the effects of these cytostatic agents on sensory fibers located in the dorsal root ganglia (DRG) in vitro and studied whether nerve growth factor (NGF) could reverse the cytostatic induced morphological changes on intact DRG (1 DRG/well, n = 10 per dose). Neuritogenesis from DRG was measured with an image analysis system following exposure to different concentrations of cytostatic drugs in the presence of 3 ng NGF/ml and cytosine arabinoside (Ara-C, 10(-6) M). Relative neurite outgrowth in intact DRG in culture was reduced dose-dependently, (a) by vincristine starting at a dose of 0.4 ng/ml for 2 days (-33% as compared to control; P < 0.001, Student's t-test); (b) by taxol 10 ng/ml (-60%; P < 0.001), and (c) by cisplatin 3 micrograms/ml (-47%, P < 0.001). Cisplatin also prevented the migration of satellite cells away from the intact DRG along the extending neurites into the well in contrast to control, vincristine, or taxol. To evaluate the neuroprotective potential of NGF in this in vitro cytostatic neuropathy model, we incubated intact DRG with cytostatic agents in combination with increasing amounts of NGF. Neurite outgrowth from DRG treated with vincristine (0.5 ng/ml)+NGF (3 ng/ml) for 2 days was significantly higher (+87%) than after treatment with vincristine + 1 ng NGF/ml (P < 0.001). Neurite outgrowth from DRG treated with taxol (20 ng/ml)+NGF (3 ng/ml) for 2 days was significantly higher (+228%) than after taxol + 1 ng NGF/ml (P < 0.05). Neuritogenesis from DRG treated with cisplatin (2.5 micrograms/ml)+NGF (3 ng/ml) for 2 days was significantly increased (+105%) compared to treatment with cisplatin + 1 ng NGF/ml (P < 0.001). DRG thus appear to be a very suitable model for studying cytostatic drug-induced neuropathies in vitro and NGF has a clear neuroprotective effect on the vincristine-, taxol-, and cisplatin-induced neuropathies in this in vitro model.

Animals↗
PubMed1991

Depletion of brain serotonin differently affects behaviors induced by 5HT1A, 5HT1C, and 5HT2 receptor activation in rats.

5-hydroxytryptamine (5HT)-depleted rats were subjected to behavioral experiments in which the response to activation of 5HT1A, 5HT1c, and 5HT2 receptor subtypes was measured. Depletion of 5HT was produced by unilateral intracerebroventricular injection of 5,7-dihydroxytryptamine (100 micrograms/rat) or by systemic injection of p-chlorophenylalanine (150 mg/kg injected intraperitoneally 72, 48, and 24 h before the test). The dose-response curve of the 5HT1A-mediated, 8-hydroxy-2-(di-n-propylamino)tetralin (0.022-0.46 mg/kg)-induced lower lip retraction was not changed after depletion, nor was the dose-response curve of the 5HT2 receptor-mediated (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (0.046-1.0 mg/kg)-induced head shake response. The dose-response curve for penile erections, a 5HT1c receptor-mediated response after mCPP (0.1-1.0 mg/kg), a direct 5HT1c agonist, is shifted to the left after 5HT depletion, whereas the response to indirect activation of the 5HT1c receptor with the 5HT reuptake inhibitors citalopram (2.2-4.6 mg/kg) and paroxetine (0.22-2.2 mg/kg) was inhibited after 5HT depletion. These results suggest that 5HT1c receptors are more subject to denervation supersensitivity than 5HT1A and 5HT2 receptors. This lesion model may be useful to discriminate behaviorally between direct and indirect activation of the 5HT1c receptor.

5,7-Dihydroxytryptamine↗
PubMed1990

Behavioural pharmacology of trans-5-chloro-2-methyl-2,3,3a,12b-tetrahydro- 1H-dibenz[2,3:6,7]oxepino-[4,5-c]pyrrolidine maleate, a compound interacting with dopaminergic and serotonergic receptors.

trans-5-Chloro-2-methyl-2,3,3a,12b-tetrahydro-1H- dibenz[2,3:6,7]oxepinol[4,5-c]pyrrolidine maleate (Org 5222) is a new compound with effects on animal behaviour indicating strong antipsychotic potential based on antagonism of dopaminergic and serotonergic effects. The compound inhibits apomorphine-induced climbing behaviour, mouse locomotor activity, rat activity in an open field, shuttle box behaviour in rats, pergolide induced circling in 6-hydroxydopamine(6-OHDA) lesioned rats, serotonin agonist-induced forepaw treading, head shakes and penile erections. The compound is less effective in inducing catalepsy, and antagonising SKF-38393 (tetrahydro- 1-phenyl-1H-3-benzazepine-7,8-diol HCl)-induced circling in 6-OHDA-lesioned rats and it does not induce perioral movements in rats. Based on these data and the neurochemical profile of the compound it was decided that this compound merits clinical investigation in a programme aiming for an effective antipsychotic agent with reduced risks of extrapyramidal side-effects.

Animals↗
PubMed1989

Ovariectomy and subchronic estradiol-17 beta administration decrease dopamine D1 and D2 receptors in rat striatum.

Ovariectomy and subchronic estradiol-17 beta cause a down-regulation of dopamine D1 and, to a lesser extent, D2 receptors in rat striatum. An intracellular mechanism mediates the DA receptor down-regulation, as various estrogens do not interact with membrane-bound DA receptors in vitro. A common denominator, e.g. enhanced DA turnover, is suggested to mediate the estradiol-induced DA receptor down-regulation. Ovarian factors other than estradiol are additionally proposed to be involved in the regulation of striatal DA receptors.

Animals↗
PubMed1988

Effect of metergoline, fenfluramine, and 8-OHDPAT on catalepsy induced by haloperidol or morphine.

The influences of the indirect serotonin agonist fenfluramine (5; 10 mg/kg s.c.), the serotonin antagonist metergoline (5; 10 mg/kg s.c.) and the 5-HT1A agonist 8-OHDPAT (0.1; 0.2; 0.46 mg/kg s.c.) on haloperidol-induced catalepsy in rats or mice and on morphine-induced catalepsy in rats were studied. Morphine-induced catalepsy was enhanced by fenfluramine and attenuated by metergoline, whereas neither fenfluramine nor metergoline had any effect on haloperidol-induced catalepsy. 8-OHDPAT strongly antagonised catalepsy induced by morphine or haloperidol. We conclude that serotonergic transmission plays a major role in effectuating morphine catalepsy but not in effectuating haloperidol catalepsy. The antagonistic effect of 8-OHDPAT suggests a secondary, modulating role for 5-HT1A receptor mediated events in both types of catalepsy.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1987

Facilitation of amphetamine-induced rotation by muscarinic antagonists is correlated with M2 receptor affinity.

This study examined the relationship between the affinity of cholinergic drugs for muscarinic receptor subtypes and their potency in potentiating or inhibiting amphetamine-induced rotation. The ascending nigrostriatal dopaminergic pathway was unilaterally lesioned in male Wistar rats using 6-hydroxydopamine. In these rats, ipsiversive rotation induced by amphetamine sulphate (1 mg/kg, s.c.) was dose-dependently inhibited by the cholinergic agonists oxotremorine, RS86 and pilocarpine and by the acetylcholinesterase inhibitor physostigmine. In contrast the cholinergic antagonists scopolamine, secoverine and dicyclomine facilitated amphetamine-induced rotation. Agonist and antagonist potencies were then compared with M1 and M2 binding site affinities estimated by displacing [3H]pirenzepine from forebrain and [3H]QNB from brainstem homogenates. The data suggest a relationship between antagonist potency and M2 binding site affinity.

Animals↗
PubMed1986

Effects of ACTH and related peptides on medial septal self-stimulation.

The effects of ACTH1-24, ACTH4-10, the ACTH4-9 analog Org 2766 and [D-Phe7] ACTH4-10 on medial septal self-stimulation were determined in the rat following intracerebroventricular (ICV) injections. Self-stimulation rates were increased by 0.01-10 micrograms ACTH1-24 or 0.1-10 micrograms ACTH4-10, but not by Org 2766 or [D-Phe7] ACTH4-10. A dose of 1 microgram ACTH1-24 ICV did not affect open field behaviour. Subcutaneous administration of 1 microgram ACTH1-24 did not influence self-stimulation in the septum. Thus, the ACTH1-24 effect appears to be a central effect and provides evidence for an influence of ACTH containing pathways on structures involved in maintaining self-stimulation behavior. A possible role of opiate receptors and dopaminergic neurons in this effect of ACTH1-24 is also discussed.

Adrenocorticotropic Hormone↗
PubMed1984

Response changes after repeated low apomorphine: dopamine autoreceptor desensitization or learning?

Repeated injection of rats with low doses of apomorphine (APO), which selectively interact with dopamine (DA) autoreceptors, caused a change in yawning responses that suggests initial low-APO-induced desensitization of DA autoreceptors, followed by a long-lasting rebound hypersensitivity. Repeated treatment with low APO followed by open-field testing, however, yielded totally different results. APO accelerated intrasession response decrement and upon repeated administration enhanced the intersession response decrement. Both for yawning and open-field behavior, the response change after the second dose of APO was only evident when the first as well as the second APO injection were followed by exposure of the rat to the same test situation. These results indicate that response changes after repeated treatment with low APO are not due to a simple DA-agonist-induced change in receptor sensitivity but that drug experience combined with environmental influences play a decisive role.

Animals↗
PubMed1983

Pharmacological aspects of mianserin.

S(+)-mianserin is the more potent enantiomer of mianserin in pharmacological tests indicative for antidepressant activity. Pharmacological tests indicative for sedation suggest that sedative effects are similar for mianserin and its enantiomers. Racemic mianserin had the optimal therapeutic ratio of antidepressant-like activity versus sedative properties when assessed by computerised EEG in healthy volunteers participating in a double-blind placebo-controlled single dose trial. Of the known metabolites, desmethylmianserin and 8-hydroxymianserin substantially retain pharmacological properties indicative for antidepressant activity but are less active than mianserin in tests indicative for sedation. Mianserin-N-oxide is inactive or only weakly active in most pharmacological tests. Desmethylmianserin occurs in human plasma after both single and multiple dosage to an extent of about one-third that of mianserin. Mianserin has optimal clinical efficacy as the racemate. Desmethyl-mianserin and 8-hydroxymianserin are pharmacologically active metabolites and may contribute to the overall antidepressant effects of mianserin.

Adult↗
PubMed1982

Alterations in local cerebral glucose utilization during chronic treatment with an ACTH 4-9 analog.

Adrenocorticotrophic hormone (ACTH) and structural analogs of the fragment ACTH4-9 have marked effects upon behavior (particularly in relation to memory processes). The effects of the chronic (10 day) administration of the potent analog (Met(O2)4,D-Lys8,Phe9]ACTH4-9(100 microgram/kg per day i.p,) upon local cerebral glucose utilization have been examined using the autoradiographic 2-deoxyglucose technique in the attempt to identify the neuroanatomical sites involved functionally in the central actions of this ACTH4-9 analog. Of the 49 anatomically discrete regions examined, significant increases in glucose utilization were observed only in the hippocampus (stratum molecular lacunosum lacunosum and parasubiculum, increased by 16 and 17% respectively), the anterior nucleus of the thalamus (by 23%) and anterior cingulate cortex (by 30%). The highly localized alterations in glucose utilization which were observed following treatment with this ACTH4-9 analog provide evidence for the functional involvement of a hippocampal-anterior-thalamic-anterior cingulate cortical circuit in the actions of this peptide fragment.

Adrenocorticotropic Hormone↗
PubMed1975

Re-introduction and evaluation of an accurate, high capacity bioassay for melanocyte-stimulating hormone using the skin of Anolis carolinensis in vitro.

A simple and rapid assay for the quantitative determination of melanocyte-stimulating hormone (MSH) activity, using skin fragments of the lizard Anolis carolinensis in vitro, is described in detail. This assay, in which a quantal response (e.g. induction of a brownish-green colour) can be detected by visual observation, allows determination of MSH activity in up to 50 samples/day by one person, using the skin of one lizard. The mean dose found to induce this colour change was 0-15 ng synthetic alpha-MSH/ml (range 0-02-0-5 ng/ml). The assays shows high accuracy, reproducibility and specificity. Anterior and posterior lobe hormones as well as pituitary catecholamines do not interfere with the determination of pituitary MSH activitymthe method is compared with the assay using hypophysectomized frogs (Rana pipiens) in vivo. Determinations of MSH in pituitary extracts by both methods gave quantitatively similar results when determined with alpha-MSH as the reference substance. However, when beta-seryl MSH was used as a reference, the two assays gave different results for the MSH activity of the pituitary extractsmthis indicates that MSH from the rat pituitary gland has a biological activity similar to that of alpha-MSH rather than to that of beta-seryl MSH.

Adrenocorticotropic Hormone↗