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Cholinergic Antagonists (cholinergic + antagonist)
Selected AbstractsEffect of halothane on type 2 immobility-related hippocampal theta field activity and theta-on/theta-off cell dischargesHIPPOCAMPUS, Issue 1 2003Brian H. Bland Abstract Rats were studied in acute and chronic (freely moving) recording conditions during exposure to different levels of the volatile anesthetic halothane, in order to assess effects on hippocampal theta field activity in the chronic condition and on theta-related cellular discharges in the acute condition. Previous work has shown that the generation of hippocampal type 2 theta depends on the coactivation of cholinergic and GABAergic inputs from the medial septum. Based on these data and recent findings that halothane acts on interneuron GABAA receptors, we predicted that exposure of rats to subanesthetic levels would result in the induction of type 2 theta field activity. In the chronic condition, exposure to subanesthetic levels of halothane (0.5,1.0 vol %) was found to induce theta field activity during periods of immobility (type 2 theta) with a mean increase of 39% in amplitude (mV) compared to control levels during movement. The total percentage of signal power (V2) associated with peak theta frequencies (80% compared to control levels of 47%) was also increased by halothane. Over the whole range of administered halothane concentrations, theta field frequency progressively declined from a mean peak frequency of 6.5 ± 0.8 Hz at 0.5 vol % halothane to a mean peak frequency of 4.0 ± 1.8 Hz at 2.0 vol % halothane. Subsequent administration of a muscarinic cholinergic antagonist, atropine sulfate, selectively abolished all type 2 immobility-related theta field activity, while type 1 movement-related theta was still intact. At anesthetic levels (1.5,2.0 vol %) in acute experiments, hippocampal field activity spontaneously cycled between theta and large-amplitude irregular activity. Analysis of depth profiles in four experiments revealed they were identical to those previously described for rats under urethane anesthesia conditions. In addition, the discharge properties of 31 theta-related cells, classified as tonic and phasic theta-on and tonic and phasic theta-off cells, did not differ significantly from those described previously in rats anesthetized with urethane. These data provide further support for an involvement of GABAA receptors in the generation of hippocampal theta. Hippocampus 2003;13:38,47. © 2003 Wiley-Liss, Inc. [source] Hippocampal structure and the action of cholinomimetic drugsDRUG DEVELOPMENT RESEARCH, Issue 3 2002John G. Csernansky Abstract Cholinomimetic drugs have become the clinical standard for the treatment of patients with dementia of the Alzheimer type (DAT). However, uncertainty remains as to the proportion of patients that respond to such drugs, and how one might predict the capacity for response before treatment is begun. The thesis of the present review is that the neuroanatomical integrity of the hippocampus determines, at least in part, the capacity of DAT patients to respond to cholinomimetic drugs. Neuroimaging studies suggest that volume losses and other neuroanatomical deformities of the hippocampus are common in patients with even mild DAT. Moreover, more severe neuroanatomical deformities of the hippocampus are associated with more severe dementia symptoms and more rapid clinical decline. Animal research, including studies of cholinergic antagonists, glutamatergic antagonists, hippocampal lesions, and animals with mutant amyloid precursor protein genes, demonstrate that behavioral abnormalities similar to those found in DAT patients, especially those related to memory, are associated with hippocampal pathology. Cholinomimetic drugs, in particular, the cholinesterase inhibitors, have been shown to reverse some but not all of these behavioral abnormalities. More research is needed in DAT patients to determine whether an analysis of hippocampal structure or function can reliably predict the outcome of treatment with cholinomimetic drugs. Further work in animals is also needed to determine the limitations of cholinomimetic drugs for reversing various types of cognitive deficits, and to develop and test other pharmacological strategies for the treatment of DAT. Drug Dev. Res. 56:531,540, 2002. © 2002 Wiley-Liss, Inc. [source] Anthelmintic paraherquamides are cholinergic antagonists in gastrointestinal nematodes and mammalsJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2002Erich W. Zinser Oxindole alkaloids in the paraherquamide/marcfortine family exhibit broad-spectrum anthelmintic activity that includes drug-resistant strains of nematodes. Paraherquamide (PHQ), 2-deoxoparaherquamide (2DPHQ), and close structural analogs of these compounds rapidly induce flaccid paralysis in parasitic nematodes in vitro, without affecting adenosine triphosphate (ATP) levels. The mechanism of action of this anthelmintic class was investigated using muscle tension and microelectrode recording techniques in isolated body wall segments of Ascaris suum. None of the compounds altered A. suum muscle tension or membrane potential. However, PHQ blocked (when applied before) or reversed (when applied after) depolarizing contractions induced by acetylcholine (ACh) and the nicotinic agonists levamisole and morantel. These effects were mimicked by the nicotinic ganglionic blocker mecamylamine, suggesting that the anthelmintic activity of PHQ and marcfortines is due to blockade of cholinergic neuromuscular transmission. The effects of these compounds were also examined on subtypes of human nicotinic ACh receptors expressed in mammalian cells with a Ca2+ flux assay. 2DPHQ blocked nicotinic stimulation of cells expressing ,3 ganglionic (IC50 , 9 µm) and muscle-type (IC50 , 3 µm) nicotinic cholinergic receptors, but was inactive at 100 µm vs. the ,7 CNS subtype. PHQ anthelmintics are nicotinic cholinergic antagonists in both nematodes and mammals, and this mechanism appears to underlie both their efficacy and toxicity. [source] | ||||||||||