Methanandamide (MAEA), the stable analog of the endocannabinoid anandamide, has been proven in Xenopus oocytes to allosterically inhibit the function of the ␣7-nicotinic acetylcholine receptors (nAChRs) in a cannabinoid (CB) receptorindependent manner. The present study aimed at demonstrating that this mechanism can be activated in vivo. In anesthetized and vagotomized pithed rats treated with atropine, we determined the tachycardic response to electrical stimulation of preganglionic sympathetic nerves via the pithing rod or to i.v. nicotine (0.7 mol/kg) activating nAChRs on the cardiac postganglionic sympathetic neurons. MAEA (3 and 10 mol/kg) inhibited the electrically induced tachycardia (maximally by 15-20%; abolished by the CB 1 receptor antagonist AM 251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide]; 3 mol/kg) in pentobarbitone-anesthetized pithed rats, but not in urethane-anesthetized pithed rats, which, thus, are suitable to study the CB 1 receptorindependent inhibition of nicotine-evoked tachycardia. The subunit-nonselective nAChR antagonist hexamethonium (100 mol/kg) and the selective ␣7-subunit antagonist methyllycaconitine (MLA; 3 and 10 mol/kg) decreased the nicotineinduced tachycardia by 100 and 40%, respectively (maximal effects), suggesting that nAChRs containing the ␣7-subunit account for 40% of the nicotine-induced tachycardia. MAEA (3 mol/kg) produced an AM 251-insensitive inhibition (maximum again by 40%) of the nicotine-induced tachycardia. Simultaneous or sequential coadministration of MLA and MAEA inhibited the nicotine-induced tachycardia to the same extent (maximally by 40%) as each of the drugs alone. In conclusion, according to nonadditivity of the effects, MAEA mediates in vivo inhibition by the same receptors as MLA, namely ␣7-subunit-containing nAChRs, although at an allosteric instead of the orthosteric site.

Background and purpose:We examined whether cannabinoid CB1 and histamine H3 receptors resemble a2-adrenoceptors in that their presynaptically mediated cardiovascular effects are less marked in urethane-than in pentobarbitone-anaesthetized pithed rats. Experimental approach: Effects of the cannabinoid agonist CP-55,940 and the H3 receptor agonist imetit on electrically induced tachycardic and vasopressor responses, respectively, was compared in pithed rats anaesthetized with urethane or pentobarbitone. The affinity of urethane for the three receptors was measured by radioligand binding studies in rat brain cortex membranes and its potency assessed in superfused mouse tissues preincubated with 3 H-noradrenaline. Key results: The neurogenic tachycardic response was less markedly inhibited by CP-55,940 in urethane-than in pentobarbitone-anaesthetized pithed rats. Imetit inhibited the neurogenic vasopressor response after pentobarbitone but not after urethane. The catecholamine-induced tachycardic and vasopressor response did not differ between rats anaesthetized with either compound. Urethane 10 mM (plasma concentration reached under anaesthesia) did not affect binding to CB1 or H3 receptors and a2 adrenoceptors, nor did it alter the inhibitory effect of agonists at the three receptors on electrically evoked 3 H-noradrenaline release. Conclusions and implications:Urethane, but not pentobarbitone, abolished the H3 receptor-mediated vascular response in pithed rats and attenuated the CB1 receptor-mediated cardiac response much more than pentobarbitone. The weaker effects of CB1, H3 and a2 receptor agonists cannot be explained by antagonism by urethane at the three receptors in vitro. Pentobarbitone, but not urethane, is suitable as an anaesthetic for investigations of inhibitory presynaptic receptor function in pithed and anaesthetized rats. (2009) British Journal of Pharmacology IntroductionPithed animals offer the opportunity to study the influence of pre- (Armstrong and Boura, 1973) and postsynaptic receptors (Shipley and Tilden, 1947) on cardiovascular parameters under conditions that resemble the in vivo situation in many respects. One major advantage of such preparations is the fact that basal blood pressure and heart rate (HR) are very stable since they are no longer under the control of reflex loops involving the central nervous system (CNS). Prior to pithing, the animals have to be anaesthetized. The choice of the anaesthetic is of crucial importance on the effect of test drugs on cardiovascular parameters studied later in the pithed animal. For instance, in pithed rats the cardiovascular responses to a2-adrenoceptor agonists acting at pre-and postsynaptic a2-adrenoceptors wereCorrespondence: E Schlicker,

The present study was carried out to examine whether acute experimental myocardial infarction affects the sympathetic transmission to vessels and the heart of pithed rats via a presynaptic mechanism and, if so, to check whether inhibitory presynaptic cannabinoid (CB) receptors and endocannabinoids are involved in this response. In pithed and vagotomized rats, electrical stimulation (0.75 Hz; 1 ms; 50 V; 5 or 15 pulses for increases in heart rate or blood pressure, respectively) of the preganglionic sympathetic nerve fibers or intravenous injection of isoprenaline (0.1 nmol/kg) or noradrenaline (1 nmol/kg) increased heart rate and blood pressure by approximately 50 beats/min and 40 mm Hg, respectively. Ligation of the left coronary artery reduced the electrically (as opposed to the chemically) induced tachycardic and pressor responses by approximately 30 to 40%. The inhibitory effect of myocardial infarction was prevented by the CB 1 receptor antagonist rimonabant but not by the CB 2 receptor antagonist N- [(1S)-endo-1,3,3-trimethyl-bicyclo[2 Our results demonstrate that during the early phase of myocardial infarction the activation of presynaptic CB 1 receptors by endogenously formed cannabinoids contributes to the inhibition of the neurogenic tachycardic and vasopressor responses. Thus, the CB 1 receptor-mediated inhibition of excessive noradrenaline release from the sympathetic nerve fibers innervating the heart and vessels might play a protective role in myocardial ischemia. .2.1]heptan-2-yl]-5-(4-chloro-3-

α7-nACh is one of the major nicotinic cholinergic receptor subtypes found in the brain. It is broadly expressed in the hippocampal and cortical neurons, the regions which play a key role in memory formation. Although α7-nACh receptors may serve as postsynaptic receptors mediating classical neurotransmission, they usually function as presynaptic modulators responsible for the release of other neurotransmitters, such as glutamate, γ-aminobutyric acid, dopamine, and norepinephrine. They can, therefore, affect a wide array of neurobiological functions. In recent years, research has found that a large number of agonists and positive allosteric modulators of α7-nAChR induce beneficial effects on learning and memory. Consistently, mice deficient in chrna7 (the gene encoding α7-nAChR protein), are characterized by memory deficits. In addition, decreased expression and function of α7-nAChR is associated agoniwith many neurological diseases including schizophrenia, bipolar disorder, learning disability, attention deficit hyperactivity disorder, Alzheimer disease, autism, and epilepsy. In the recent years many animal experiments and clinical trials using α7-nAChR ligands were conducted. The results of these studies strongly indicate that agonists and positive allosteric modulators of α7-nAChR are promising therapeutic agents for diseases associated with cognitive deficits.