Search results for "Autoreceptor"
showing 9 items of 29 documents
Cholinergic–Adrenergic Presynaptic Interactions in the Heart and Characterization of the Receptors Involved
1991
ABSTRACT The rabbit perfused atria preparation with the extrinsic sympathetic and vagus innervation intact has been used to study the mutual interactions between the two branches of the autonomic nervous system by measuring the respective transmitter overflow rates upon electrical stimulation. Using this method the stimuli exciting vagus and sympathetic nerves can be applied at selected time intervals which provides an advantage over the common method of field stimulation where all kinds of neurons are stimulated simultaneously. In the absence of drugs, presynaptic interactions resulting in a decreased noradrenaline overflow occurred when the vagal stimuli preceded the sympathetic ones by 3…
Characterization of prejunctional muscarinic autoreceptors in the guinea-pig trachea
1991
1. The effects of ten muscarinic antagonists on electrically evoked [3H]-acetylcholine release and muscle contraction were compared in an epithelium-free preparation of the guinea-pig trachea that had been preincubated with [3H]-choline. 2. The M3-selective antagonists UH-AH 37, 4-diphenyl-acetoxy-N-piperidine methobromide and para-fluorohexahydrosiladiphenidol were more potent in reducing the contractile response than in facilitating the evoked [3H]-acetylcholine release. Hexahydrosiladiphenidol did not discriminate between pre- and postjunctional effects. The rank order of the postjunctional potencies of the ten antagonists as well as the postjunctional pA2 values obtained for hexahydrosi…
Inhibitory and excitatory muscarinic receptors modulating the release of acetylcholine from the postganglionic parasympathetic neuron of the chicken …
1992
The effects of muscarinic receptor antagonists on ACh release were studied in the absence or presence of cholinesterase (ChE) inhibition using the isolated perfused chicken heart. Presynaptic inhibitory muscarinic autoreceptor were characterized by determining the potency of various antagonists to enhance [3H]-ACh release evoked by field stimulation (3 Hz, 1 min). The order of potencies was: (±)-telenzepine > atropine > 4-DAMP > silahexocyclium > pirenzepine > hexahydro-siladifenidol > AF-DX 116. The comparison with known pA2 values for M1-, M2- and M3-receptors revealed that the presynaptic autoreceptor meets the criteria of an M1-receptor. Basal, not electrically evoked overflow of unlabe…
The role of vagus activity in the presynaptic control of noradrenaline release from rabbit atria.
1990
Abstract On various heart preparations with the autonomic innervation left intact, vagus nerve stimulation (VNS) has been found to reduce the amount of noradrenaline (NA) that is released in response to sympathetic nerve stimulation (SNS). The following experiments were carried out on an innervated rabbit perfused atria preparation in which the overflow of NA and acetylcholine (ACh) could be determined simultaneously. VNS impulses applied at a fixed time interval before the corresponding SNS impulses reduced NA overflow when the interval was 3–10 ms (early peak) or 200–283 ms (late peak of inhibition). VNS applied 30–167 ms before SNS had no significant effect (“ineffectual period”). Both i…
Lack of autoreceptor mediated regulation of the spontaneous dopamine turnover in the isolated neurointermediate lobe of the rat pituitary gland in vi…
1990
Isolated neurointermediate lobes of the rat pituitary gland were incubated in Krebs-HEPES solution and the spontaneous outflow of endogenous dopamine and its metabolites (DOPAC, HVA and MOPET) was determined by HPLC with electrochemical detection. The spontaneous outflow of dopamine metabolites (about 1500 fmol/10 min) largely exceeded that of dopamine (about 60 fmol/10 min). Apomorphine concentration-dependently (IC50, 205 nmol/l) reduced the spontaneous outflow of the dopamine metabolites. The effect of apomorphine developed slowly and was progressive over an observation period of 70 min. After 1 h of exposure to a maximall effective concentration of apomorphine (10 mumol/l), the outflow …
Characterization of endogenous noradrenaline release from intact and epithelium-denuded rat isolated trachea.
1991
1. Overflow of endogenous noradrenaline (NA) from the in vitro incubated rat trachea evoked by two periods of electrical field stimulation (S1, S2 at 3 or 15 Hz) or by high potassium (60 mM) was determined by high performance liquid chromatography (h.p.l.c.) with electrochemical detection. 2. In the presence of the neuronal uptake inhibitor desipramine, the alpha 2-adrenoceptor antagonist, yohimbine, enhanced the overflow of NA evoked by stimulation at 3 Hz by about 100% suggesting the presence of presynaptic inhibitory autoreceptors on the sympathetic nerves innervating the trachea. 3. When desipramine and yohimbine were present throughout the experiments, the overflow of NA evoked by the …
Pre- and Postjunctional Muscarinic Receptors in the Guinea-pig Trachea
1991
ABSTRACT The effects of M2- and Me-selective muscarinic antagonists on electrically evoked [3H]acetylcholine release and muscle contraction were compared in the isolated guinea-pig trachea. The M2-selective antagonists methoctramine and AF-DX 116 were more potent in enhancing the evoked release than in inhibiting the contractile response. As a consequence of the selective blockade of the inhibitory autoreceptors the evoked muscle contractions were enhanced by low concentrations (0.1 μmol/l) of the M2-selective antagonists. The Me-selective antagonists 4-DAMP, UH-AH 37 and pFHHSiD were more potent in reducing the contraction than in facilitating the evoked release. Surprisingly, HHSiD did no…
Dopamine agonists in schizophrenia: a review.
1995
Although it is unlikely that the different types of course and severity of schizophrenia are caused by one neurochemical abnormality alone, indirect pharmacological evidence still suggests a relative excess of dopaminergic activity being implicated in the pathogenesis of most of the schizophrenic symptoms, e.g. positive symptomatology. Synthesis and release of dopamine as well as firing rates of dopaminergic neurons are controlled by stimulation of autoreceptors via a negative feedback regulation. Investigations on therapeutic effects of autoreceptor-nonselective dopamine agonists in schizophrenia have yielded inconsistent results. Dopamine autoreceptor agonists like pramipexole, roxindole,…
Psychotropic Effect of Combined Estrogen-Vit B6 Treatment in Endogenously Depressed Females
1985
Estrogens are among the most commonly prescribed substances in females. Also endogenous estrogen levels change dramatically throughout life and this biological variable has been associated with several psychological signs like premenstrual tension syndrome and depression in older age. Along with clinical practice there is increasing evidence from neuropharmacology suggesting a psychotropic action of estrogens (review: Holsboer, 1982). The most prominent findings are: 1. Reduction of monoamine-oxidase (MAO)-activity by estrogens (McEwen et al., 1978); 2. Competitive inhibition of catechol-o-methyltransferase by 2-hydroxyestrogens, which are major metabolites of estrogens in the CNS (Breuer e…