Lack of CB1receptors increases noradrenaline release in vas deferens without affecting atrial noradrenaline release or cortical acetylcholine release

We studied whether cannabinoid CB1 receptor gene disruption (to yield CB1−/− mice) affects the electrically evoked tritium overflow from vas deferens and atrial pieces preincubated with [3H]-noradrenaline (NA) (‘noradrenaline release') and from cerebral cortex slices preincubated with [3H]-choline (‘acetylcholine release'). NA release was higher by 37% in vas deferens from CB1−/− mice than in vas deferens from CB1+/+ mice. The cannabinoid receptor agonist WIN 55,212-2 inhibited, and the CB1 receptor inverse agonist/antagonist SR 141716, increased NA release in vas deferens from CB1+/+ mice without affecting it in vas deferens from CB1−/− mice. Atrial NA release did not differ between CB1+/+ and CB1−/− mice nor did WIN 55,212-2 affect NA release in either strain. Cortical acetylcholine (Ach) release did not differ between CB1+/+ and CB1−/− mice. WIN 55,212-2 inhibited, but SR 141716 did not affect, Ach release in the cortex from CB1+/+ mice. Both drugs did not alter Ach release in the cortex from CB1−/− mice. Tritium content did not differ between CB1+/+ and CB1−/− mice in any preparation. In conclusion, the increase in NA release associated with CB1 receptor deficiency in the vas deferens, which cannot be ascribed to an alteration of tritium content of the preparations, suggests an endogenous tone at the CB1 receptors of CB1+/+ mice in this tissue. Furthermore, the effect of WIN 55,212-2 on NA release in the vas deferens and on cortical Ach release involves CB1 receptors, whereas the involvement of non-CB1–non-CB2 receptors can be excluded. Keywords: Cerebral cortex, vas deferens, atrium, acetylcholine release, noradrenaline release, cannabinoid CB1 receptors, CB1 receptor-deficient mouse, presynaptic receptors, SR 141716 Introduction Cannabinoid CB1 receptors serve as presynaptic inhibitory receptors on a variety of central and peripheral neurones (for review, see Schlicker & Kathmann, 2001; Howlett et al., 2002). These receptors are activated by endocannabinoids like anandamide, 2-arachidonoylglycerol, noladin ether and virodhamine (Hanus et al., 2001; Porter & Felder, 2001; Porter et al., 2002). Many types of presynaptic CB1 receptors appear to be subject to an endogenous tone as suggested by the fact that CB1 receptor inverse agonists/antagonists like SR 141716 facilitate the release of the respective neurotransmitter (for review, see Pertwee, 1999; Schlicker & Kathmann, 2001). It is of interest in this context whether lack of CB1 receptors will lead to the same result. We have indeed found recently (Kathmann et al., 2001b) that in hippocampal slices, in which SR 141716 increases acetylcholine (Ach) release (Kathmann et al., 2001a), the release of this transmitter was also increased by CB1 receptor deficiency (CB1 receptor knockout mouse (CB1−/−) generated by Zimmer et al. (1999) from C57BL/6J mice). This alteration in transmitter release is very specific inasmuch as hippocampal noradrenaline (NA) release and striatal Ach release (both of which are not subject to modulation via CB1 receptors; Schlicker et al., 1997; Kathmann et al., 2001a) did not differ between both strains (Kathmann et al., 2001b). The aim of the present study was to examine whether parallel effects of SR 141716 and of CB1 receptor deficiency also occur in other isolated tissues of the mouse. For this purpose, we determined the influence of CB1 receptor gene disruption on NA release in the vas deferens and in the atrium. NA release in the vas deferens is inhibited via presynaptic CB1 receptors subject to an endogenous tone (Rinaldi-Carmona et al., 1994; Pertwee et al., 1996), whereas atrial NA release is not affected by presynaptic CB1 receptors at all (Trendelenburg et al., 2000). Our study was extended to cerebral cortex slices in which Ach release was determined. This experimental model differs from the latter two and from the models considered in our previous study (Kathmann et al., 2001b) in that the release of the transmitter is inhibited via presynaptic CB1 receptors, which are, however, not subject to an endogenous tone, that is, Ach release is not facilitated by SR 141716 (Kathmann et al., 2001a).