Anandamide and NADA bi‐directionally modulate presynaptic Ca²⁺ levels and transmitter release in the hippocampus

Abstract

stores, and fatty acid metabolism. AEA was recently reported to block TASK-3 potassium channels thereby depolarizing membranes. Common inhibitors of TASK-3, Zn 2 þ , Ruthenium Red, and low pH mimicked the excitatory effects of AEA and NADA, suggesting that their effects on [Ca 2 þ ] i and transmitter levels may be attributable to membrane depolarization upon TASK-3 blockade. The K þ -evoked Ca 2 þ entry and Ca 2 þ -dependent transmitter release were inhibited by nanomolar concentrations of the CB 1 receptor agonist WIN55212-2; this action was sensitive to the selective CB 1 receptor antagonist AM251. However, in the low micromolar range, WIN55212-2, NADA and AEA inhibited the K þ -evoked Ca 2 þ entry and transmitter release independently of CB 1 receptors, possibly through direct Ca 2 þ channel blockade. Conclusions and implications: We report here for hybrid endocannabinoid/endovanilloid ligands novel dual functions which were qualitatively similar to activation of CB 1 or TRPV 1 receptors, but were mediated through interactions with different targets.

Regulation of Hippocampal Cannabinoid CB1 Receptor Actions by Adenosine A1 Receptors and Chronic Caffeine Administration: Implications for the Effects of Δ9-Tetrahydrocannabinol on Spatial Memory

“…AM251 (1 mM) fully blocked the effect of 1 mM, but not of 10 mM of WIN55,212-2 ( Figure 1c). Higher concentrations of AM251 were not used to avoid loss of selectivity (see Köfalvi, 2007Köfalvi, , 2008. The enantiomer had no significant effect applied at 1 mM, but it inhibited evoked [ 3 H]GABA release by 22.4 ± 1.4% at 10 mM (n ¼ 5, po0.05; Figure 1c), which indicates that the effect of 1 mM WIN55,212-2 upon [ 3 H]GABA release is CB 1 receptor dependent.…”

“…In control conditions, pooling data from all experiments performed, the average basal release of [ 3 H]GABA from rat hippocampal synaptosomes was 0.76 ± 0.02% (n ¼ 31, average of first 6 min of collection; Figure 1a) of the total tritium retained by synaptosomes at the same time points. Depolarization of the hippocampal synaptosomes with K + (15 mM) for 2 min induced a threefold increase in the [ 3 H]GABA release with an average peak of 2.5 ± 0.1% during S 1 , and 2.3 ± 0.1% (n ¼ 31; Figure 1a) To induce a CB 1 receptor-dependent effect on [ 3 H]GABA release, we used the potent cannabinoid receptor agonist WIN55,212-2, which has been previously shown to inhibit evoked [ 3 H]GABA release from hippocampal synaptosomes through a CB 1 -specific mechanism, having a maximum CB 1 -selective effect at 1 mM (Köfalvi et al, 2007). Application of 1 mM WIN55,212-2 6 min before S 2 caused a decrease of basal [ (Figure 1c).…”

TRPV1 acts as a synaptic protein and regulates vesicle recycling

“…Capsaicin has been shown to alter synaptic transmission in the rat medial preoptic nucleus, a hypothalamic area that regulates body temperature (Kauer and Gibson, 2009;Karlsson et al, 2005). N-arachidonoyl-dopamine (NADA), an agonist for TRPV1, is known to modulate the presynaptic Ca 2+ levels and transmitter release in the hippocampus (Huang et al, 2002;Starowicz et al, 2007b;Tóth et al, 2009;Köfalvi et al, 2007). Although all these reports support a function of TRPV1 at synapses, direct evidence for the presence of TRPV1 in synapses is lacking.…”

Presynaptic TRPV1 vanilloid receptor function is age- but not CB1 cannabinoid receptor-dependent in the rodent forebrain

“…Lack of TRPV 1 R-triggered release of radiolabeled neurotransmitters from synaptosomal preparations (D'Amico et al, 2004;Köfalvi et al, 2005Köfalvi et al, , 2007Cannizzaro et al, 2006;Ferreira et al, 2009) can be a result of the age of the animals used and/or of the lack of temporal resolution of the technique itself, i.e. that a fast-desensitizing capsaicin effect (Baamonde et al, 2005) is diluted in the minute-scale sampling process.…”