piperidines and tripitramine

Striatal m4 muscarinic receptors are important because their blockade controls movement, and they are preferentially located on striatal neurons that project to the internal globus pallidus. The following studies were performed in vitro to provide a basis for using antimuscarinic toxins to study the effects of selective m4 blockade on movement in vivo. Because m4-toxin has limited selectivity alone (102-fold higher affinity for m4 than m1 receptors), m1-toxin was used first to occlude m1 receptors selectively, fully and irreversibly. It blocked 42% of the sites for 1.0 nM 3H-N-methylscopolamine in rat striatal membranes and 43% in sections of cat striatum. m4-Toxin (>500-fold higher affinity for m4 than m2, m3 or m5 receptors) blocked 88% of the residual, non-m1 sites in membranes, showing 64 pmol m4 receptors/g tissue. In comparison, AFDX-116, biperiden, clozapine, gallamine, hexahydrodifenidol, himbacine, R(+)hyoscyamine, methoctramine, pirenzepine, silahexocyclium, trihexyphenidyl and tripitramine did not distinguish m4 from other non-m1 receptors. 3H-Pirenzepine dissociated twice as rapidly from non-m1 as m1 receptors. Autoradiography was used to test the idea that m4 receptors are localized preferentially in the striosomes of the cat striatum. Non-m1 receptors were distributed equally in striosomes and matrix, indicating that striatal neurons with m4 receptors are in both compartments. Thus m1-toxin facilitates studies of m4 receptors by occluding m1 receptors, and m4-toxin is a selective antagonist for residual m4 receptors.

Topics: Alkaloids; Animals; Benzodiazepines; Binding, Competitive; Cats; CHO Cells; Corpus Striatum; Cricetinae; Elapid Venoms; Furans; Gallamine Triethiodide; Humans; Male; Muscarinic Antagonists; N-Methylscopolamine; Naphthalenes; Neurotoxins; Piperidines; Pirenzepine; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Receptor, Muscarinic M4; Receptors, Muscarinic; Recombinant Proteins

To clarify which muscarinic receptor subtype(s) mediate changes in sleep and cortical temperature (Tcort) induced by carbachol microinjections into the medial preoptic area (MPA), pirenzepine, tripitramine and +/- p < > -fluorohexahydro-sila-difenidol (p-F-HHSiD), which are highly selective muscarinic M1, M2 and M3 antagonists, respectively, were microinjected into the MPA of rats. Whereas pirenzepine (3.45 and 7.08 nmol) and p-F-HHSiD (3.90 and 7.80 nmol) were without effect, tripitramine (0.67 and 3.37 nmol) enhanced wakefulness, decreased slow wave and desynchronized sleep, and raised Tcort with the higher dose. The data suggest that in the MPA only M2 muscarinic subtypes may be functionally important in mediating the cholinergic effects on sleep and thermoregulation.

Topics: Animals; Benzodiazepines; Body Temperature Regulation; Male; Microinjections; Muscarinic Antagonists; Piperidines; Pirenzepine; Preoptic Area; Rats; Receptors, Muscarinic; Sleep; Sleep, REM; Wakefulness

Several novel methoctramine-related tetraamines were designed, and their biological profiles at muscarinic receptor subtypes were assessed by functional experiments in isolated guinea pig and rat atria (M2) and smooth muscle (ileum and trachea, M3) and by binding assays in rat cortex (M1), heart (M2), and submaxillary gland (M3) homogenates and NG 108-15 cells (M4). Tripitramine, a nonsymmetrical tetraamine, resulted in the most potent and the most selective muscarinic M2 receptor antagonist of the series (pA2 = 9.14-9.85; pKi = 9.54). Spirotramine (FC 15-94), a symmetrical tetraamine, was able to differentiate between muscarinic M1 receptors (pKi = 7.88) and the other subtypes (M2, pKi = 6.20; M3, pKi = 5.81; M4, pKi = 6.27). Thus, tripitramine and spirotramine could be valuable tools for the pharmacological classification and characterization of muscarinic receptor subtypes.

Topics: Animals; Atrial Function; Benzodiazepines; Benzodiazepinones; Diamines; Drug Design; Guinea Pigs; Heart Atria; Ileum; Muscarinic Antagonists; Muscle Contraction; Muscle, Smooth; Parasympatholytics; Piperidines; Pirenzepine; Rats; Receptors, Muscarinic; Structure-Activity Relationship; Submandibular Gland; Trachea